1. Field of the Invention
The present invention relates to a method for removing coronene deposits from a heat exchange zone of a reforming process.
2. Description of the Prior Art
Reforming is a well known process in which a hydrocarbonaceous feedstock, such as naphtha, is contacted at elevated temperature and pressure in the presence of added hydrogen with a solid catalyst to increase the aromaticity of the feedstock. See, for example, Hydrocarbon Processing, September 1976, pages 171-178. The effluent of the reforming zone comprises undesired polycyclic aromatic compounds, including coronene, in amounts which vary depending on the operating conditions. Coronene (C.sub.24 H.sub.12) is a polycyclic aromatic compound having a structure which contains 7 benzene rings in a circular pattern with no side chains. Its molecular weight is 300 and its melting point is 440.degree. C. Because of its high melting point, when coronene is present in relatively high concentrations, coronene readily deposits as a solid upstream of the effluent dew point in the heat exchanger used to cool the effluent.
U.S. Pat. No. 3,332,842 discloses recycling a portion of the gasoline reformate to the total reaction effluent prior to separating the reaction product into gaseous phase and liquid phase to minimize catalyst deactivation caused by polycyclic aromatic compounds such as coronene.
U.S. Pat. No. 1,672,801 discloses the use of a solvent, such as naphtha, to dissolve asphalt in clogged drawoff pipes or separation zones of hydrocarbon conversion processes.
U.S. Pat. No. 3,725,247 discloses that polynuclear aromatics which have a deleterious effect on the catalyst are formed during hydrocracking. It teaches treatment of the catalyst to avoid formation of polyaromatic compounds.
U.S. Pat. No. 2,953,514 relates to a method of reducing heat exchanger fouling. It discloses injecting a portion of the liquid reformate boiling at least above 450.degree. F. in the stream of the reactor effluent at a point upstream of the heat exchanger.
It has now been found that by maintaining the dew point of the effluent of the reformer at a dew point temperature such that at least a portion of the effluent condenses to a liquid in the fouled portion of heat exchanger, the deposit of coronene in the heat exchanger can be removed.